Sera from Clinical Center patients with AIDS continued to be monitored for antibodies to Toxoplasma gondii and Entamoeba histolytica and were found to be similar to those you would expect to find in any group of non-AIDS patients. Toxoplasma has been isolated from brain tissue of 5 AIDS patients at autopsy. A method has been developed to detect filarial antigen in circulating immune complexes of patients with filariasis. The method is not influenced by rheumatoid, anti-nuclear and other non-specific factors sometimes contained in serum. The method will not detect circulating unbound antigen so that the antigen detected is only antigen which was dissociated from the polyethylene glycol precipitated immune complexes. Antigen was found in complexes from 9 of 32 sera from filariasis patients in India and in 5 of 12 sera tested from filariasis patients in the Cook Islands. These sera were previously found to have been circulating immune complexes by both the Clq-ELISA and 125I-Clq binding assay. In addition sera from a patient with no demonstrable filarial antigen complexes before treatment with diethylcarbamazine had antigen detected in immune complexes after initiation of treatment. The method provides a method of evaluating immune complexes in these patients as to whether or not the complexes are related to filariais or are due to some other factors not related to filariasis.